The present invention relates to a recording and reproducing apparatus for recording and reproducing data using a laser disk, a compact disk, or other optical disk.
More specifically, the present invention relates to a signal generation method used in an optical disk reproducing apparatus for reproducing data recorded on an optical disk by using a beam of light (spot) to scan along a land and guide groove provided on the optical disk, which detects a tracking error signal representing the position of the spot of the beam of light with respect to a guide groove provided in the optical disk and a cross track signal of a phase advanced by 90xc2x0 relative to the tracking error signal, and to an apparatus of the same.
Also, the present invention relates to an optical pick-up using this signal generation method.
Further, the present invention relates to an optical disk recording and reproduction method using the tracking signal and the cross track signal obtained by the above method to control the tracking servo from an off state to a tracking-on state, that is, so-called tracking servo pull-in control, and to an apparatus using the same.
FIG. 1 is a schematic view of the configuration of an optical disk reproducing apparatus of a differential push-pull system. The optical disk reproducing apparatus of the differential push-pull system illustrated in FIG. 1 comprises an optical disk 2 on which the data is recorded, a spindle motor 4 for rotating the optical disk 2, an optical pick-up 6, a control processor unit 8, and a drive amplifier unit 10.
FIG. 2 is a view of the configuration of the optical system of the optical pick-up 6 illustrated in FIG. 1.
In FIG. 1 and FIG. 2, the optical pick-up 6 has mounted on it a laser 61, a collimator lens 62, a diffraction lattice 63, a beam splitter 64, an objective lens 65, a focus lens 66, a photodetector and processor unit 67, a tracking coil 68, and a focus coil 69.
The laser 61, collimator lens 62, diffraction lattice 63, beam splitter 64, objective lens 65, and focus lens 66 constitute an optical system which directs a spot to the optical disk 2 and guides the reflected light of the spot from the optical disk 2 to the photodetector and processor unit 67.
This optical pick-up 6 is an optical pick-up of a two-axis drive system. In this optical pick-up, large movement in the track direction of the optical disk 2 is carried out by using a carriage (not shown) on which the optical pick-up 6 is mounted. After the optical pick-up 6 mounted on the carriage moves to the vicinity of the target position of the optical disk 2, a tracking coil 68 is used for positioning to the precise track position.
FIG. 3 is a view illustrating a method of detecting the position of a beam (spot) of light irradiated on the lands and grooves of the optical disk 2 and the reflected light of the beam of light at the photodetector and processor unit 67 mounted on the optical pick-up 6 illustrated in FIG. 2 and generating a tracking error signal and a cross track signal from the detection signal when the width of the lands and the width of the guide grooves (hereinafter referred to as the xe2x80x9cgroovesxe2x80x9d) in the optical disk 2 are different.
The photodetector and processor unit 67 has a first side photodetector (or second photodetector) 671, a center photodetector (main photodetector or first photodetector) 672, and a second side photodetector (or third photodetector) 673. The photodetector and processor unit 67 further has a signal processor unit 675.
The first side photodetector 671 and the second side photodetector 673 are each comprised of split photodetectors having two sections in the track direction of the optical disk 2. The center photodetector 672 is comprised of a split photodetector having four sections in the track direction (radial direction) and tangential direction (circumferential direction) of the optical disk 2.
In this way, FIG. 2 and FIG. 3 illustrate an example of optical disk 6 of the three-point optical detection system using three types of beams of light (three spots of light) and three types of photodetectors 671 to 673.
The signal processor unit 675 has a signal input unit 675A for receiving as its inputs detection signals from the photodetectors 671 to 673, a focus error signal processor unit 675B for calculating a focus error signal FE from the input signals, a tracking error signal processor unit 675C for calculating a tracking error signal TE, a cross track signal processor unit 675D for calculating a cross track signal CTS, and a sum signal processor unit 675E for calculating a sum signal PI.
It is also possible to perform the signal processing of the signal processor unit 675 at the control processor unit 8, but a case where it is performed in the photodetector and processor unit 67 will be explained below.
The control processor unit 8 has three analog/digital (A/D) converters 81 to 83, two normalization circuits 84 and 85, two phase compensation digital filters 86 and 87, and two digital/analog (D/A) converters 88 and 89.
The processing inside the control processor unit 8 is carried out in a digital manner by using for example a digital signal processor (DSP), therefore the A/D converters 81 to 83 convert the analog signals from the photodetector 67 to digital signals and convert the processing results of the DSP to analog signals suited for the drive amplifier unit 10 at the D/A converters 88 and 89.
The drive amplifier unit 10 has two drive amplifiers 101 and 102.
The first drive amplifier 101 is used for controlling the drive of the focus coil 69 in the optical pick-up 6, while the second drive amplifier 102 is used for controlling the drive of the tracking coil 68 in the optical pick-up 6.
The configuration of the first side photodetector 671, the center photodetector 672, and the second side photodetector 673 in the photodetector unit 67 illustrated in FIG. 3 is also applied to embodiments of the present invention. However, as is apparent from the description given later, the conditions of the land width and the groove width in the optical disk 2 and the positional relationship of the spots differ between the related art and the present invention.
The general operation of the optical disk reproducing apparatus of the differential push-pull system illustrated in FIG. 1 and FIG. 2 will be explained referring to FIG. 3 as well.
In the optical system illustrated in FIG. 2, one beam of laser light emitted from the laser 61 is converged at the collimator lens 62 and made to strike the diffraction lattice 63. The diffraction lattice 63 diffracts the beam of light from the collimator lens 62 to generate three beams of light and makes them strike the beam splitter 64. The three diffracted beams striking the beam splitter 64 pass through the beam splitter 64 to strike the objective lens 65. In the objective lens 65, they are then converged to the lands and the grooves of the optical disk 2 as spots (indicated by the circles in FIG. 3).
The spots of the beam of light irradiated to the lands or grooves of the optical disk 2 are reflected from the lands or grooves to return to the objective lens 65, then enter from the objective lens 65 into the beam splitter 64. At the beam splitter 64, they are directed toward the focus lens 66 and are received at photodetectors 671, 672, and 673 of the photodetector unit 67.
The spots on the optical disk 2 have different phases according to the lands or grooves. The amounts of light striking the photodetectors 671 to 673 are therefore different.
The photodetectors 671 and 672 detect the amounts of incident light. The focus error signal processor unit 675B, tracking error signal processor unit 675C, cross track signal processor unit 675D, and sum signal processor unit 675E perform the following processing on the detected values and calculate the focus error signal FE, tracking error signal TE, cross track signal CTS, and sum signal PI.
When the analog focus error signal FE, tracking error signal TE, and sum signal PI (or RF signal) are output from the photodetector unit 67 (photodetectors 671 to 673), the A/D converters 81 to 83 at the control processor unit 8 convert these analog signals to digital signals.
The focus error signal FE converted at the A/D converter 81 and the sum signal PI converted at the A/D converters 81 to 83 are supplied to the normalization circuit 84 where the focus error signal FE is divided by the sum signal PI to normalize the focus error signal FE. Similarly, the tracking error signal TE converted at the A/D converter 82 and the sum signal PI converted at the A/D converter 83 are supplied to the normalization circuit 85 where the tracking error signal TE is divided by the sum signal PI to normalize the tracking error signal TE.
The normalized focus error signal FE is phase compensated at the phase compensation digital filter 86. Similarly, the normalized tracking error signal TE is phase compensated at the phase compensation digital filter 87. The D/A converters 88 and 89 convert the phase-compensated focus error signal FE and tracking error signal TE to analog signals.
The phase-compensated focus error signal converted to the analog signal at the D/A converter 88 is amplified at the drive amplifier unit 101 and drives the focus coil 69 mounted on the optical pick-up 6. Due to this, the position of the objective lens 65 of the optical pick-up 6 is controlled with respect to the optical disk 2 so that the focus has an error of 0.
In the same way as the above, the phase-compensated tracking error signal converted to an analog signal at the D/A converter 89 is amplified at the drive amplifier unit 102 and supplied to the tracking coil 68. By this, the track position of the optical pick-up 6 is controlled so that the positional deviation (track error) of the optical unit 2 in the track direction (radial direction) becomes 0.
In this way, the control processor unit 8 is basically constituted by the focus control system comprising the A/D converter 81, normalization circuit 84, phase compensation digital filter 86, and D/A converter 88 and the tracking control system comprising the A/D converter 82, normalization circuit 85, phase compensation digital filter 87, and D/A converter 89.
Note that the focus control system is not the theme of the present invention, therefore a detailed description thereof will be omitted. Accordingly, a detailed explanation of the method of calculation of the focus error signal FE will be omitted also. These are equivalent to those of the related art.
The A/D conversion, normalization, and phase compensation in the control processor unit 8 explained above were only explained in brief. Details will be explained in the embodiments of the present invention.
First, an explanation will be given of the positions of the spots on the optical disk 2 and the method of generation of the tracking error signal TE and cross track signal CTS by the differential push-pull system in the signal processor unit 675 of the photodetector and processor unit 67.
The diffraction lattice 63 mounted on the optical pick-up 6 forms three beams from the single beam emitted from the laser 61 and converged at the collimator lens 62 and irradiates the optical disk 2 with three spots.
As illustrated in FIG. 3, in this example, the two side spots, that is, the first side spot S1 and second side spot S2, are located shifted by xc2xd of the land pitch in the radial direction relative to the main spot SM on the optical disk 2.
At this time, the differential push-pull signal of the main spot SM (hereinafter referred to as the main push-pull signal) ((A+D)xe2x88x92(B+C)), the differential push-pull signal of the first side spot S1 (hereinafter referred to as the first side push-pull signal) (Exe2x88x92F), and the differential push-pull signal of the second side spot S2 (hereinafter referred to as the second side push-pull signal) (Gxe2x88x92H) are shifted in phase by exactly 180xc2x0 relative to the position in the tracking direction of the optical disk 2 as illustrated in FIG. 4.
In order to make the amplitude of the main push-pull signal and the amplitude of the sum of the first and second side push-pull signals ((Exe2x88x92F)+(Gxe2x88x92H)) match, the sum of the first and second side push-pull signals Is amplified by exactly the ratio of the amount of light with respect to the main push-pull signal (the amplification gain at this time is defined as xcex1), the sum of the two side push-pull signals amplified by the ratio of the amount of light is subtracted from the main push-pull signal ((A+D)xe2x88x92(B+C)), and the result is defined as the tracking error signal TE illustrated in FIG. 6. The equation for calculating the tracking error signal TE is shown below:
TE=((A+D)xe2x88x92(B+C))xe2x88x92xcex1((Exe2x88x92F)+(Gxe2x88x92H))xe2x80x83xe2x80x83(1)
The focus error signal FE is calculated by for example the following equation:
FE=((Axe2x88x92C)+(Bxe2x88x92D))xe2x80x83xe2x80x83(2)
In the three-point spot method, the push-pull signal is not only defined by the position of the main spot SM relative to the lands on the optical disk 2, but is also defined by the positions of the side spots S1 and S2 relative to the grooves. In other words, in the three-point spot method, the push-pull signal is not only defined by the detection value of the center photodetector 672, but is also defined by the detection values of the side photodetector 671 and 673.
For this reason, if only using the main push-pull signal ((A+D)xe2x88x92(B+C)) as the tracking error signal TE=((A+D)xe2x88x92(B+C)), the correct tracking error signal TE cannot be obtained when the objective lens 65 is moved corresponding to the eccentricity of the optical disk 2.
Contrary to this, in the differential push-pull system shown in equation 1, there is the advantage that signals resulting from the positions of the spots on the photodetectors 671 to 673 cancel each other out when finding the difference of the push-pull signals and that only the correct tracking error signal TE shown in FIG. 6 is obtained.
As illustrated in FIG. 6, there are two positions of spots where the tracking error signal TE becomes 0, i.e., on a land and on a groove in the optical disk 2. Accordingly, since the positions of the spots cannot be differentiated by just the tracking error signal TE, a signal for discriminating between them becomes necessary. This signal is referred to as the cross track signal CTS. The method of calculation will be explained next.
As illustrated in FIG. 3, where the land width of the optical disk 2 is made wider than the groove width, as illustrated in FIG. 5, the sum signal (A+B+C+D) of the main spot becomes the largest on the land, and the smallest on the groove. By utilizing this relationship and finding the difference between the sum signal (A+B+C+D) of the main spot and the sum signal (E+F+G+H) of a side spot multiplied by an amplification gain xcex1 of the amount of the ratio of the amount of light (following equation 3), a cross track signal CTS with a phase advanced 90xc2x0 relative to the tracking error signal TE illustrated in FIG. 6 is found.
CTS=(A+D+B+C)xe2x88x92xcex1(E+F+G+H)xe2x80x83xe2x80x83(3)
Since the difference between the sum signal (A+D+B+C) of the main spot and the sum signal (E+F+G+H) of a side spot multiplied by the coefficient xcex1 is found for calculation of the cross track signal CTS, even if the total amounts of light received change at the positions of the spots etc. at the photodetectors 671 to 673, they cancel each other out and a cross track signal CTS with a high precision is obtained.
The tracking error signal TE is processed at the tracking error signal processor unit 675C illustrated in FIG. 3, the cross track signal CTS is processed at the cross track signal processor unit 675D, and the focus error signal FE is processed at the focus error signal processor unit 675B.
In the optical disk 2 illustrated in FIG. 3, the land width is wider than the groove width and data is recorded only in the grooves, but as one procedure for improving the recording density of the optical disk, the xe2x80x9cland and groove recording methodxe2x80x9d which records data on both of the lands and grooves of the optical disk has been known.
Summarizing the problem to be solved by the invention, in order to optimize the recording and reproduction characteristic in the land and groove recording method, it is necessary to make the width of the lands and the width of the grooves the same.
In this case as well, the correct tracking error signal TE is obtained from the conditions of equation 1, but the sum signal of the side spot in the above explanation becomes equal on the lands and on the grooves as illustrated in FIG. 7 and a cross track signal CTS can no longer be generated by equation 3. Namely, the above method of calculation of a cross track signal cannot be used in the land and groove recording method for improving the recording density of the optical disk when the land width and the groove width are made the same. In other words, when the land width and the recording width are made the same in the land and groove recording method, the problem is encountered that the phase of the tracking error signal TE cannot be differentiated and pull-in in tracking control is not possible.
An object of the present invention is to provide a method and an apparatus capable of correctly generating not only a tracking error signal and focus error signal, but also a cross track signalxe2x80x94even in a case where the land width and the groove width are equal in the land and groove recording method used for improving the recording density of the optical disk.
Another object of the present invention is to provide an optical disk recording and reproducing apparatus improving the density of an optical disk by applying the above method and apparatus to an optical pick-up.
Still another object of the present invention is to provide an optical disk recording and reproducing method capable of control of the tracking servo from an off state to a tracking on state, i.e., so-called tracking pull-in control, using the tracking signal and cross track signal obtained by the above method.
In the present invention, the arrangement of the spots and the method of signal processing are tinkered with to enable not only the tracking error signal and focus error signal, but also the cross track signal to be correctly obtained even in the land and groove recording method in which the land width and the groove width are equal.
According to a first aspect of the present invention, there is provided a signal generation method for positioning a main spot to be radiated on an optical disk and side spots of the two sides of the main spot on lands and grooves of the optical disk, detecting the reflected light of the main spot and side spots, and calculating a track error signal and a cross track signal shifted by a predetermined phase relative to the track error signal, comprising detecting the reflected light of the main spot by a first photodetector split into four sections in the track direction and tangential direction of the optical disk, detecting the reflected light of a first side spot at one side of the main spot by a second photodetector split into two sections in the track direction of the optical disk, and detecting the reflected light of a second side spot at the other side of the main spot by a third split into two sections in the track direction of the optical disk and calculating a first error as an error in the radial direction of the optical disk from four detection signals detected by the first photodetector, calculating a second error as an error of two detection signals of the second photodetector, calculating a third error as an error of two detection signals of the third photodetector, calculating the tracking error signal by subtracting from the first error the sum of the second and third errors, and finding the difference between the second error and the third error to calculate the cross track signal.
The land width and the groove width in the optical disk may be equal and the side spots at the two sides of the main spot positioned exactly a predetermined distance of less than xc2xd of the land pitch away from the main spot in the radial direction of the optical disk.
Preferably, the side spots at the two sides of the main spot are positioned exactly a predetermined distance of xc2xc of the land pitch away from the main spot in the radial direction of the optical disk.
Alternatively, the land width and the groove width in the optical disk may be different.
According to a second aspect of the present invention, there is provided such a signal generation method used for an optical disk recording and reproduction apparatus.
The cross track signal may be used for discrimination of the state of the tracking error signal.
Alternatively, the cross track signal and the tracking error signal may be used to calculates the speed of movement and position of an optical pick-up with respect to the optical disk.
In this case, the calculated speed of movement and position may be used for judging tracking pull-in.
Alternatively, the cross track signal and tracking error signal may be used for judgement of tracking pull-in.
According to a third aspect of the present invention, there is provided an optical pick-up for positioning a main spot to be radiated on an optical disk and side spots of the two sides of the main spot on lands and grooves of the optical disk, detecting the reflected light of the main spot and side spots, and calculating a track error signal and a cross track signal shifted by a predetermined phase relative to the track error signal, comprising a first photodetector split into four sections in the track direction and tangential direction of the optical disk and receiving the reflected light of the main spot, a second photodetector split into two sections in the track direction of the optical disk and receiving the reflected light of a first side spot at one side of the main spot, a third photodetector split into two sections in the track direction of the optical disk and receiving the reflected light of a second side spot at the other side of the main spot, an optical system for directing the main spot and the two side spots to the optical disk and leading the reflected light of the main spot and the side spots to the first to third photodetectors, and a signal processing means for calculating a first error as an error in the radial direction of the optical disk from four detection signals detected by the first photodetector, calculating a second error as an error of two detection signals of the second photodetector, calculating a third error as an error of two detection signals of the third photodetector, calculating the tracking error signal by subtracting from the first error the sum of the second and third errors, and finding the difference between the second error and the third error to calculate the cross track signal.
Preferably, further provision is made of a tracking coil and focus coil.
The land width and the groove width in the optical disk may be equal and the optical system may position the side spots at the two sides of the main spot exactly a predetermined distance of less than xc2xd of the land pitch away from the main spot in the radial direction of the optical disk.
Preferably, the optical system positions the side spots at the two sides of the main spot exactly a predetermined distance of xc2xc of the land pitch away from the main spot in the radial direction of the optical disk.
The land width and the groove width in the optical disk may also be different.
According to a fourth aspect of the present invention, there is provided an optical disk recording and reproducing apparatus provided with an optical disk on which lands and grooves are formed adjoining each other in the radial direction; an optical pick-up able to move relative to the optical disk in the track direction of the optical disk; and a control means for tracking control of the optical pick-up with respect to the optical disk in accordance with a detection signal from the optical pick-up; the optical pick-up having a first photodetector split into four sections in the track direction and tangential direction of the optical disk and receiving the reflected light of the main spot, a second photodetector split into two sections in the track direction of the optical disk and receiving the reflected light of a first side spot at one side of the main spot, a third photodetector split into two sections in the track direction of the optical disk and receiving the reflected light of a second side spot at the other side of the main spot, an optical system for directing the main spot and the two side spots to the optical disk and leading the reflected light of the main spot and the side spots to the first to third photodetectors, and a signal processing means for calculating a first error as an error in the radial direction of the optical disk from four detection signals detected by the first photodetector, calculating a second error as an error of two detection signals of the second photodetector, calculating a third error as an error of two detection signals of the third photodetector, calculating the tracking error signal by subtracting from the first error the sum of the second and third errors, and finding the difference between the second error and the third error to calculate the cross track signal having a predetermined phase difference from the tracking error signal and the control means using the tracking error signal and cross track signal for tracking control.
Preferably, the signal processing means of the optical pick-up further calculates at least a focus error signal from the four signals of the first photodetector, the optical pick-up has a focus coil, and the control means uses the focus error signal for focus control.
The land width and the groove width in the optical disk may be equal and the side spots at the two sides of the main spot positioned exactly a predetermined distance of less than xc2xd of the land pitch away from the main spot in the radial direction of the optical disk.
Preferably, the side spots at the two sides of the main spot are positioned exactly a predetermined distance of xc2xc of the land pitch away from the main spot in the radial direction of the optical disk.
The land width and the groove width in the optical disk may also be different.
The cross track signal may be used for discrimination of the state of the tracking error signal.
Alternatively, the cross track signal and the tracking error signal may be used to calculate the speed of movement and position of the optical pick-up with respect to the optical disk.
The speed of movement and position of the optical pick-up may be used for judgement of tracking pull-in.
The cross track signal and tracking error signal may also be used for judgement of tracking pull-in.
According to a fifth embodiment of the present invention, there is provided an optical disk recording and reproducing apparatus provided with an optical disk on which lands and grooves are formed adjoining each other in the radial direction; an optical pick-up able to move relative to the optical disk in the track direction of the optical disk; and a control means for tracking control of the optical pick-up with respect to the optical disk in accordance with a detection signal from the optical pick-up; the optical pick-up having a first photodetector split into four sections in the track direction and tangential direction of the optical disk and receiving the reflected light of the main spot, a second photodetector split into two sections in the track direction of the optical disk and receiving the reflected light of a first side spot at one side of the main spot, a third photodetector split into two sections in the track direction of the optical disk and receiving the reflected light of a second side spot at the other side of the main spot, an optical system for directing the main spot and the two side spots to the optical disk and leading the reflected light of the main spot and the side spots to the first to third photodetectors, and a tracking coil, the control means calculating a first error as an error in the radial direction of the optical disk from four detection signals detected by the first photodetector, calculating a second error as an error of two detection signals of the second photodetector, calculating a third error as an error of two detection signals of the third photodetector, calculating the tracking error signal by subtracting from the first error the sum of the second and third errors, and finding the difference between the second error and the third error to calculate the cross track signal having a predetermined phase difference from the tracking error signal and the control means using the tracking error signal and cross track signal for tracking control.
In short, the tracking error signal and cross track signal generated as explained above are used for the tracking control in the optical disk recording and reproducing apparatus.
For example, the cross track signal is used for the differentiation of the state of the tracking error signal. Further, the speed of movement and position of the optical pick-up with respect to the optical disk are calculated by using the cross track signal and the tracking error signal. The speed of movement and position calculated in this time are used to judge the tracking pull-in. Further, the tracking pull-in is controlled by using the cross track signal and the tracking error signal.